1. Field of the Invention
The present invention is directed to a new class of microoptical systems and methods for fabricating such microoptical systems and, more particularly, to a method of fabricating in situ, on a surface, through the use of a lithographic process, a plurality of micro-scale optical elements.
2. Description of the Prior Art
Microoptical systems that combine micro-scale optical elements, such as lenses, mirrors, beamsplitters, apertures, prisms, fiber optics, and optical couplers, have capabilities far greater than can be achieved with a single micro-scale optical element. In particular, microoptical systems with clear aperture of about one millimeter or less are required for a number of applications, including medical and biochemical diagnostics, optical fiber switching, and optical data processing. Microoptical systems for these applications typically require the precise alignment and integration of a plurality of micro-scale optical elements.
One method to produce such a microoptical system is to miniaturize a conventional optical bench. Microoptical systems can be produced by fabricating a micro-scale optical bench upon which a plurality of micro-scale optical elements are subsequently mounted and aligned in discrete mechanical devices. Post-assembly and alignment of such microoptical systems on the micro-scale to achieve a precise focus, collimation, or other optical function is extremely difficult. Because of the manifold difficulties encountered in the assembly and practical application of conventional microoptical systems, a need exists for a microoptical system wherein a plurality of micro-scale optical elements can be precisely assembled and aligned on a substrate.
The present invention solves this problem for microoptical systems having one or multiple optical axes. Micro-scale optical elements are fabricated monolithically on a common surface by a lithographic process, thereby eliminating the need for post-assembly and alignment of separate micro-scale optical elements on a micro-scale optical bench.
A description of lithographic processes can be found in Chapter 1 of Fundamentals of Microfabrication (Marc Madou, CRC Press, 1997).
According to the present invention, any photo- or charged-particle-beam lithographic process that uses a collimated beam of radiation having an absorption length on the order of several hundred microns in a high contrast resist can produce such a microoptical system. In particular, deep X-ray lithography (DXRL) typically uses a highly collimated beam of high energy X-rays from a synchrotron radiation source to achieve a large depth of focus in a thick layer of X-ray photoresist. Thus, DXRL can produce very steep radiation and photoresist profiles. Typical DXRL-produced microstructures have aspect ratios of 100 or greater, with feature heights of up to about 1 mm and sidewall surface roughness of about 10 nm RMS.